1. Field of the Invention
The present invention relates to an electronic fuel injection apparatus, and in particular to an electronic fuel injection apparatus which controls a fuel injection timing of a fuel injection pump for a diesel engine through a timing control valve.
2. Description of the Related Art
FIG. 6 shows an embodiment of an electronic fuel injection apparatus according to the present invention, which is schematically composed of an injection pump 1, an engine control computer (hereinafter abbreviated as ECC) 2, and an electromagnetic spill valve control circuit (EDU) 3.
The ECC 2 inputs an engine revolution signal from a revolution sensor 11 provided in the injection pump 1, a fuel temperature signal from a fuel temperature sensor 12, an accelerator opening signal, an intake pressure signal, a coolant temperature signal, a car speed signal, an intake temperature signal, and a crank angle signal respectively outputted from an accelerator opening sensor, a pressure sensor, a water temperature sensor, a speed sensor, an intake temperature sensor, and a crank position sensor (none of which are shown). Then, the ECC 2 performs a predetermined computation for providing a command signal CMD to the control circuit 3 of the electromagnetic spill valve and for providing a control signal to a timing control valve (hereinafter abbreviated as TCV) 24.
In addition, receiving such a command signal CMD, the control circuit 3 sends a driving signal to a solenoid 14 in an electromagnetic spill valve 13 provided in the injection pump 1.
Hereinafter, the operation of the injection pump 1, which is well known though, in such an electronic fuel injection apparatus will be briefly described.
When a drive shaft 15 rotates which is made to rotate in synchronization with the crank shaft (not shown) of the engine, a pulsar 16 rotates, so that the engine revolution speed signal is provided from the sensor 11 which detects the rotating state to the ECC 2.
A plunger 17 rotates as the drive shaft 15 rotates. When a cam plate 18 united with the plunger 17 simultaneously rotates, a cam provided in the cam plate 18 rides on an opposite and fixed roller ring 19 whereby the plunger 17 reciprocates as shown by the arrow of FIG. 6.
When the plunger 17 shifts to the right direction in FIG. 6, a fuel in a pressure chamber 20 is compressed. At this time, if the solenoid 14 of the electromagnetic spill valve 13 is made ON and an on-off valve 21 which also serves as an armature is controlled to be in the closed state as shown in FIG. 6, the fuel of the pressure chamber 20 is to be compressedly forwarded from a distribution port 22 to an injection nozzle (not shown).
In addition, since the on-off valve 21 is opened when the plunger 17 shifts to the left direction in FIG. 6 and the solenoid 14 is made OFF, the fuel of the pressure chamber 20 is pushed back to the pump chamber, so that compressedly forwarding the fuel is finished, and the fuel is again sucked from an intake port 23 to the pressure chamber 20.
Thus, controlling the OFF timing of the electromagnetic spill valve 13 determines the fuel injection quantity of the injection pump 1.
On the other hand, for a control mechanism of a fuel injection timing, are provided a timer piston 27 which moves according to an oil pressure, a slide pin 26 which connects the roller ring 19, modifying the reciprocation timing of the plunger 17 by being rotated around the plunger 17, to the timer piston 27, and the TCV 24 which adjusts the oil pressure applied to the timer piston 27. It is to be noted that FIG. 6 is shown turned by 90 degrees.
The ECC 2 controls the duty ratio of the TCV 24 whereby the timer piston 27 is moved through a pressure chamber 25 where the fuel is enclosed, the position of the timer piston 27 is determined, the position of the roller ring 19 is rotated through the slide pin 26, and the lift starting point of the cam plate 18 is controlled. Thus, an injection starting time is controlled.
For the above-mentioned control of the fuel injection timing, a so-called feedback control is performed such that a target fuel injection timing is determined from the driving state of the engine and the timing control valve 24 is controlled so that an actual fuel injection timing may approach the target fuel injection timing. As means for detecting the actual fuel injection timing, the ECC 2 computes the actual fuel injection timing from the phase difference between the crank angle signal detected from the crank position sensor provided within a crank case (not shown) and a cam angle signal detected at the revolution sensor 11 of the fuel injection pump 1.
When parts (or a mechanism) for controlling the fuel injection timing such as a TCV 24 and a revolution sensor have a fault for some cause in such an electronic fuel injection apparatus, the fuel injection timing can not be normally controlled. Therefore, the ECC 2 performs a so-called fail-safe control such as determining whether or not an abnormality occurs to perform a backup control in case of the abnormal state.
As such a control method, the methods indicated in the Japanese Patent Publication Laid-open No. 9-317542 and the Japanese Patent Publication No. 3-18023 can be cited. Those prior art methods are arranged such that the case where the difference between the target fuel injection timing and the actual fuel injection timing exceeds a predetermined value is determined abnormal.
However, in such prior art, it is possible that a fault can not be detected when fuel injection timing controlling parts have a fault in a state where the difference between the target fuel injection timing and the actual fuel injection timing does not exceed a predetermined value.
Also, when the fuel injection timing controlling parts are determined abnormal in the former Japanese Patent Publication Laid-open No. 9-317542, for the fail-safe control upon the abnormality determined, measures are considered of holding the actual fuel injection timing to a fixed value on a lag angle side or providing a limit (guard) to the target fuel injection timing so as to prevent the actual injection timing from becoming extremely large or small.
Such measures can be taken when the fuel injection timing controlling parts operate normally. However, when the controlling parts fail to operate due to the abnormality, it becomes impossible to perform a fuel injection, resulting in a problem that the fuel injection timing can not be controlled.
Furthermore, whether on the lead angle side or the lag angle side the actual fuel injection timing becomes abnormal is not clear. If the actual fuel injection timing becomes abnormal on the lead angle side, nevertheless the fuel injection similar to that on the lag angle side is performed, there has been a problem that a cylinder pressure increases and parts around a combustion chamber are damaged.